Linux Swap and Swapfile: Difference between revisions

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== Add/Remove Swapfile Short Guide ==
Swap is a space on a disk that is used when the amount of physical RAM memory is full. When a Linux system runs out of RAM, inactive pages are moved from the RAM to the swap space.
 
Swap space can take the form of either a dedicated swap partition or a swap file. In most cases when running Linux on a virtual machine (VPS) a swap partition is not present so the only option is to create a swap file.
 
== Add/Remove Swap file Short Guide ==


=== Swap On ===
=== Swap On ===
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<syntaxhighlight lang="bash" start="3">
<syntaxhighlight lang="bash" start="3">
/swapfile swap swap defaults 0 0
/swapfile swap swap defaults 0 0
</syntaxhighlight>If <code>fallocate</code> is not installed or you get an error message saying <code>fallocate failed: Operation not supported</code> then use the following command to create the swap file:<syntaxhighlight lang="shell" line="1">
</syntaxhighlight>
If <code>fallocate</code> is not installed or you get an error message saying <code>fallocate failed: Operation not supported</code> then use the following command to create the swap file:
<syntaxhighlight lang="shell" line="1" class="mlw-shell-gray">
sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
</syntaxhighlight>
</syntaxhighlight>
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=== Swap On/Off Scripts ===
=== Swap On/Off Scripts ===
<syntaxhighlight lang="shell" class="mlw-continue">
<syntaxhighlight lang="shell" class="code-continue">
swap-on.sh  
swap-on.sh  
</syntaxhighlight>
</syntaxhighlight>
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sudo free -h
sudo free -h
</syntaxhighlight>
</syntaxhighlight>
<syntaxhighlight lang="shell" class="mlw-continue">
<syntaxhighlight lang="shell" class="code-continue">
swap-off.sh  
swap-off.sh  
</syntaxhighlight>
</syntaxhighlight>
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echo
echo
sudo free -h
sudo free -h
</syntaxhighlight>
== Add/Remove Swap file Short Guide ==
Here is used the entire small (virtual desk) <code>/dev/sde</code> as swap, but you can use a partition...<syntaxhighlight lang="shell" class="code-continue" line="1">
sudo mkswap /dev/sde
</syntaxhighlight>
<syntaxhighlight lang="shell-session" start="1">
Setting up swapspace version 1, size = 4 GiB (4294963200 bytes)
no label, UUID=ad5aad68-f8ec-48be-8025-ccd3bd112e2e
</syntaxhighlight><syntaxhighlight lang="shell" class="code-continue" line="1">
sudo blkid /dev/sde
</syntaxhighlight>
<syntaxhighlight lang="shell-session" start="1">
/dev/sde: UUID="ad5aad68-f8ec-48be-8025-ccd3bd112e2e" TYPE="swap"
</syntaxhighlight><syntaxhighlight lang="shell" class="code-continue" line="1">
sudo swapon /etc/fstab
swapon --show
</syntaxhighlight>
<syntaxhighlight lang="shell-session" start="1">
NAME    TYPE      SIZE USED PRIO
/dev/sdb partition  4G  0B  -2
</syntaxhighlight><syntaxhighlight lang="shell" class="code-continue" line="1">
sudo nano /etc/fstab
</syntaxhighlight>
<syntaxhighlight lang="bash" start="1">
#/swapfile none swap sw 0 0
UUID=ad5aad68-f8ec-48be-8025-ccd3bd112e2e    none    swap    sw      0  0
</syntaxhighlight>
</syntaxhighlight>


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==References==
==References==


*[https://linuxize.com/post/how-to-add-swap-space-on-ubuntu-18-04/ How To Add Swap Space on Ubuntu 18.04]
*Linuxsize: [https://linuxize.com/post/how-to-add-swap-space-on-ubuntu-18-04/ How To Add Swap Space on Ubuntu 18.04]
*[https://askubuntu.com/q/969296/566421 How to delete a swap file in Ubuntu?]
*Ask Ubuntu: [https://askubuntu.com/q/969296/566421 How to delete a swap file in Ubuntu?]
*itBeginner.net: [https://itbeginner.net/tweak-optimize-ssd-ubuntu-linux-mint/ How to tweak and optimize SSD for Ubuntu, Linux Mint]
*Ubuntu Docs: [https://help.ubuntu.com/community/SwapFaq Swap FAQ]


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Latest revision as of 00:47, 1 May 2023

Lin­ux Desk­top
Lin­ux Serv­er

Swap is a space on a disk that is used when the amount of phys­i­cal RAM mem­o­ry is full. When a Lin­ux sys­tem runs out of RAM, in­ac­tive pages are moved from the RAM to the swap space.

Swap space can take the form of ei­ther a ded­i­cat­ed swap par­ti­tion or a swap file. In most cas­es when run­ning Lin­ux on a vir­tu­al ma­chine (VPS) a swap par­ti­tion is not present so the on­ly op­tion is to cre­ate a swap file.

Add/​​​Remove Swap file Short Guide

Swap On

sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo nano /etc/fstab

/swapfile swap swap defaults 0 0

If fal­lo­cate is not in­stalled or you get an er­ror mes­sage say­ing fal­lo­cate failed: Op­er­a­tion not sup­port­ed then use the fol­low­ing com­mand to cre­ate the swap file: 

sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576

Swap Off

sudo swapoff -a     # sudo swapoff /swapfile
sudo rm -f /swapfile
sudo nano /etc/fstab

#/swapfile swap swap defaults 0 0

Check the swap and its us­age

sudo swapon --show
sudo free -h

Swap On/​​​Off Scripts

swap-on.sh

#!/bin/bash

sudo fallocate -l 4G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo sed 's_^#/swapfile_/swapfile_' /etc/fstab -i

echo
sudo swapon --show
echo
sudo free -h

swap-off.sh

#!/bin/bash

sudo swapoff /swapfile
sudo rm -f /swapfile
sudo sed 's_^/swapfile_#/swapfile_' /etc/fstab -i

echo
sudo swapon --show
echo
sudo free -h

Add/​​​Remove Swap file Short Guide

Here is used the en­tire small (vir­tu­al desk) /​​​dev/​​​sde as swap, but you can use a par­ti­tion…

sudo mkswap /dev/sde

Setting up swapspace version 1, size = 4 GiB (4294963200 bytes)
no label, UUID=ad5aad68-f8ec-48be-8025-ccd3bd112e2e

sudo blkid /dev/sde

/dev/sde: UUID="ad5aad68-f8ec-48be-8025-ccd3bd112e2e" TYPE="swap"

sudo swapon /etc/fstab
swapon --show

NAME     TYPE      SIZE USED PRIO
/dev/sdb partition   4G   0B   -2

sudo nano /etc/fstab

#/swapfile	none	swap	sw	0	0
UUID=ad5aad68-f8ec-48be-8025-ccd3bd112e2e    none    swap    sw      0   0

Ad­just­ing the Swap­pi­ness Val­ue

Swap­pi­ness is a Lin­ux ker­nel prop­er­ty that de­fines how of­ten the sys­tem will use the swap space. Swap­pi­ness can have a val­ue be­tween 0 and 100. A low val­ue will make the ker­nel to try to avoid swap­ping when­ev­er pos­si­ble while a high­er val­ue will make the ker­nel to use the swap space more ag­gres­sive­ly.

The de­fault swap­pi­ness val­ue is 60. You can check the cur­rent swap­pi­ness val­ue by typ­ing the fol­low­ing com­mand: 

cat /proc/sys/vm/swappiness

60

While the swap­pi­ness val­ue of 60 is OK for Desk­tops, for pro­duc­tion servers you may need to set a low­er val­ue. For ex­am­ple, to set the swap­pi­ness val­ue to 10, type: 

sudo sysctl vm.swappiness=10

To make this pa­ra­me­ter per­sis­tent across re­boots ap­pend the fol­low­ing line to the /etc/sysctl.conf file: 

sudo nano /etc/sysctl.conf

vm.swappiness=10

The op­ti­mal swap­pi­ness val­ue de­pends on your sys­tem work­load and how the mem­o­ry is be­ing used. You should ad­just this pa­ra­me­ter in small in­cre­ments to find an op­ti­mal val­ue.

Ref­er­ences


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